Magnetically strong ferromagnetic magnesium-zinc type of ferrite



United States Pa t.ent v 'Ernst -Albers Schoenberg, Metuchen; N. J.,assignor to SteatiteResearclr Corporatiom Keasbey, N. J., a corporationof Delaware I N 0.- Drawing. Application Novembertzfl, .1952, Serial No.322,339

1'Clairn. (Cl. 252-62.5)

{This invention relates toga magnetically strong ferromagnetic ceramicmaterial consistingprimarily of .the magnesium zinc type of ferrite.

,.It ;is among the objects .of the-invention therefore to provide, aferritebody which is..essentially. of.,the, zincmagnesium type but whichhas strong.magneticproperties and a relatively high Curie point.

Thev ferrites comprise a group of crystal type compounds of the generalformula X(MO)Y(Fezs).:in which MO stands for one or several bivalentmetal oxides and in which X:Y is approximately 1:1. Mostofthesecompounds have a spinel structure and ferromagnetic properties.When M"O is ferrous oxidesthe ferrite is the mineral magnetite. Most ofthe ferrites which have a high permeability contain an essentialproportion of nickel oxide as "one of the bivalent metal oxides. Nickel.oxide is expensive and, restricted in war time so that it would be anadvantage to produce a ferrite with high-permeabilityproperties-withoutfthe addition' of any great amount 1 of nickel oxide.

One way of obtaining ferrites with good properties is to replace thenickel oxide by manganese oxide. Manganese zinc ferrites exhibitexcellent properties but-these ferrites have to be'fired in a strictlycontrolledaneulral atmosphere, a procedure not easily carried outespecially when large quantities of magnetic cores have to be handled.Manganese, furthermore, is not too plentiful either.

The ferrites made from the bivalent oxides of magnesium and zinc offerthe advantage that these materials are easily available and that themagnesium-zinc ferrites do not require firing in a protectiveatmosphere, i. e., ;no special precautions need to be taken to includeprotective gases nor to exclude atmospheric air duripgf-firing, coolingor other heat treatment of these ferrites. However, there is adisadvantage too, the magnesiurn-zi-neien" rites are not very strongmagnetically.

This application is a continuation-in-part of my application No.248,889, filed September 28, 1951, now Patent No. 2,670,331. In thatapplication the idea of improving the magnetic properties of themagnesium-zinc ferrites by substituting or adding a small amount ofcupric oxide is disclosed. By such an addition of 1.58% of cupric oxide,or preferably 2-5 of the latter, a significant increase in initialpermeability and saturation flux density and a great increase in maximumpermeability is attained. In that application the possibility of addingnickel oxide as an optional constituent is also disclosed.

It has been found, however, that magnesium-zinc andmagnesium-zinc-copper ferrites of high initial permeability-for a widescope of applications initial permeabilities of 600 or more arerequired-the Curi point of such compositions comes down to about 90 to95 C. When magnetic cores of such ferrites are employed in televisionsets, for example, the heat developed by the electronic tubes may raisethe temperature of the core close to the temperature of 95 C. whereuponpermeability 2,773,039 Fatnted Dec. 4, 1956 andsaturation, flux-. density.-;drop and .-as a result the :voltage. required :across thetransformereis; decreased.

,Ihisrinventionis based -onthe discoverythat arelatively minor amount ofnickel-oxide addedto the composition of said prior application increasesthe magnetic strength as well as ,the Curie temperature to an unexpecteddegree permitting the employment of the resulting ferrites in deviceswhich may develop higher temperatures. The amount of nickel oxiderequired to markedly improve the Curie point can be-as small'as 2% byweight. A maximum degree of improvement is noted with the addition of2-4% of nickel although additional improvements in properties are notedwith additions of 0ver.4.%. of nickel (up to 8%, for example).

Of course, as set forth-in said prior application any significant-amountof nickel oxide'improves the properties of the product. :However, sincethe nickel is scarce; emphasis is laid on'the fact that in'the4-bivalent oxide ferrite system MgO-NiOCuOZnOFe'zO-3 a comparativelysmallamount of nickel oxide works Qutvery effectively. I Thecopperwoxide (C140) is added -ingthe proportion of 1.257%. It may beadded as such or in the form of asalt such as the basic coppercarbonate, for example, (Cu(OH)2.2CuCO3).

-The total-proportion"of-bivalent oxides (zinc oxide, anagnesium oxide,cupricoxideand nickel oxide) 'is approximately equal to the'molproportion otFezOsbut :can vary-nfrom 1:09 to 1:11 Asmall amount (up-to3 mol percent) of lithium oxidetadded as the carbonate) may also beincluded.

The overall composit-ion of the bodymay therefore vary between theapproximatedimits shown in the followingtable:

M01, Weight,

- Percent Percent Theqinvention, both as to its organization and itsmethod-of operation, together-with additional objects and advantagesthereof, willbest beundcrstoodfrom the following description of specificembodiments -wl1en, read all} connection with the accompanying examples.

Example 1 'A mix consisting of the following ingredients in theproportions stated is wetball-milled for 15 hours, then dried, andpulverized.

Compound Weight Percent 3 7 Example 2 A prefired nickel-zinc ferritecontaining approximately 18 mol percent of nickel oxide, 30 mol percentof zinc oxide and 52 mol percent of FezOs (corresponding toapproximately 10% by weight of nickel oxide, 20% by weight of zinc oxideand approximately 70% by weight of ferric oxide) is ground to a. powderand introduced into the following composition.

Percertby Approxiweight mate mol percent 5710 3.6 Nickel-zine ealcine 20{Zn0 H6] 4 Total 100 100 (As much as 60% scrap may be employed forincorporating the required amount of nickel into the compo-" sition.)

Example 3 A mix containing the following ingredients is wet ballmilledfor hours then dried and pulverized:

Mol Weight Percent Percent MgO 8.9 3.0 ZnO 23.6 16.0 N10 10.3 6.5 has.copper carbonate- 6.2 6.0 F8203 51. 0 68.5

The whole mix is subjected to a mild prefiring process at 1050 C., thenreground, and after addition of 1% of an organic binder arid 4% ofwater, molded into suitable cores. The cores are fired in air at about1320 C. This body was tested at various temperatures from 28 C. to 150C. The Curie point is not sharp and although a maximum value of ,uO isobtained at about 120 C. the body is usable up to at least 150 C.

From the two examples it can be seen, that the relatively small amountof nickel oxide is more eflici'ent when added in the raw state, than ifit is incorporated from a calcine. As compared to a product which doesnot contain nickel, not only are the initial permeability, maximumpermeability, and saturation flux density increased by the addition ofnickel oxide but the Curie point is considerably increased over that ofabout C. for the nickel-free products. Thus the temperature range ofusefulness of the said ferrites is considerably increased. The systemMgONiO-CuOZnO--Fez0s ofiers means and ways to exploit a small amount ofnickel oxide most economically.

The features and principles underlying the invention described above inconnection with specific exemplifications will suggest to those skilledin the art many other modifications thereof. It is accordingly desiredthat the appended claim shall not be limited to any specific features ordetails shown and described in connection with the exemplificationsthereof.

I claim:

A fired ferromagnetic body of high permeability properties and having aCurie point above C. consisting essentially of the following ingredientsin the proportions indicated:

Mol percent MgO s 2s ZnO 25-14 CuO 2-11 NiO 3-12 LizO 0-3 FezOs47.4-52.4

References Cited in the file of this patent UNlTED STATES PATENTS1,997,193 Kato Apr. 9, 1935 2,565,058 Albers-Schoenberg Aug. 21, 19512,685,568 Wilson Aug. 3, 1954 OTHER REFERENCES Philips Technical Review,vol. 8, N. 12 Dec. 1946, page 355.

